Axial fan

ABSTRACT

An axial fan is disclosed herein. The axial fan may include a hub, to which a central shaft may be coupled, and a plurality of blades coupled to an outside of the hub to rotate therewith. Each blade of the plurality of blades may include a hub connection portion that defines a first end of the respective blade, the hub connection portion being coupled to an outer circumferential surface of the hub, a tip that defines a second end of the predetermined blade, a first wing that extends at a first predetermined gradient from the tip, and a second wing that extends from the first wing towards the hub, the second wing having a second predetermined gradient.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority under 35 U.S.C. 119 and 35 U.S.C. 365 to Korean Patent Application No. 10-2013-0154592, filed in Korea on Dec. 12, 2013, which is hereby incorporated by reference in its entirety.

BACKGROUND

1. Field

An axial fan is disclosed herein.

2. Background

In general, air conditioners are apparatuses for cooling or heating an indoor space. Such an air conditioner may include a compressor to compress a refrigerant, a condenser, in which the refrigerant discharged from the compressor may be condensed, an expander, in which the refrigerant passing through the condenser may be expanded, and an evaporator, in which the refrigerant expanded in the expander may be evaporated.

The condenser and the evaporator of the air conditioner may function as heat-exchangers that perform heat-exchange between the refrigerant and external air. The condenser and the evaporator may be disposed in an indoor unit or device or an outdoor unit or device. The heat-exchanger disposed in the indoor unit is called an indoor heat-exchanger, and the heat-exchanger disposed in the outdoor unit is called an outdoor heat-exchanger.

An axial fan to blow air toward the outdoor heat-exchanger may be disposed in or at one side of the outdoor heat-exchanger disposed in or at the outdoor unit. The axial fan may include a hub connected to a rotational shaft of a motor, and a plurality of blades coupled to an outside of the hub. When the axial fan is rotated by driving a motor, a pressure difference is generated between front and rear surfaces of the plurality of blades. A suction force which allows air to flow is generated due to the pressure difference.

Thus, external air is suctioned into the outdoor unit by the suction force of the axial fan. The external air passes through the heat-exchanger disposed at a side of an air suction hole of the outdoor unit. The external air is heat-exchanged with the refrigerant flowing into the heat-exchanger to allow the refrigerant to be condensed or evaporated, and then, the external air is discharged out of the outdoor unit by the blowing operation of the axial fan.

The axial fans according to the related art include a hub coupled to a central shaft thereof, and a plurality of blades coupled to an outer surface of the hub. The central shaft is rotatably coupled to a motor.

The hub has an approximately cylindrical shape. Also, the hub has a front surface portion that defines a front surface, a rear surface portion that defines a rear surface, and an outer circumferential surface portion, to which the plurality of blades are coupled. Each of the plurality of blades includes a hub connection part or portion coupled to the outer circumferential surface portion of the hub, and a tip that defines an end of the blade.

In the axial fans according to the related art, the hub may have a relatively large diameter in comparison to a total diameter of the axial fan. For example, the hub may have a diameter of about 30% to about 35% of the total diameter of the axial fan. In this case, the axial fan may be deteriorated in efficiency due to a flow separation phenomenon, and noise may be generated.

That is, as the outer circumferential surface of the hub is disposed in a direction parallel to a flow direction of air, friction with air may be generated. Thus, the flow separation phenomenon occurs at the outer circumferential surface of the hub due to the friction. In addition, a strong vortex is generated by the flow separation phenomenon, and flow losses of the fan and strong noise occur by the vortex.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements, and wherein:

FIG. 1 is a view of an outdoor unit according to an embodiment;

FIGS. 2 to 4 are views of an axial fan according to an embodiment;

FIG. 5 is a cross-sectional view taken along line V-V of FIG. 2;

FIG. 6 is a view of a hub connection part of a blade according to an embodiment;

FIG. 7 is a view of first and second wing parts of the blade according to an embodiment;

FIGS. 8A to 8C are views illustrating a shape of a pitch angle of a blade according to embodiments, when the second wing part is not adopted in the blade;

FIGS. 9A to 9C are views illustrating a shape of a pitch angle of a blade according to embodiments, when the second wing part is adopted in the blade;

FIG. 10 is a graph of results obtained by comparing changes in power consumption of an axial fan according to the related art and an axial fan according to an embodiment;

FIG. 11 is a graph of results obtained by comparing changes in noise of an axial fan according to the related art and an axial fan according to an embodiment;

FIG. 12 is a graphic view illustrating vorticity occurring around an axial fan when the axial fan according to the related art operates; and

FIG. 13 is a graphic view illustrating vorticity occurring around an axial fan when the axial fan according to an embodiment operates.

DETAILED DESCRIPTION

Hereinafter, embodiments will be described with reference to the accompanying drawings. Embodiments may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, alternate embodiments included in other retrogressive inventions or falling within the spirit and scope will fully convey the concept to those skilled in the art.

FIG. 1 is a view of an outdoor unit according to an embodiment. Referring to FIG. 1, an outdoor unit or device 10 of an air conditioner according to an embodiment may include a case 11, a heat-exchanger 20, an axial fan 100, a motor, a compressor 40, and a blocking plate 50. The blocking plate 50 may be disposed to partition an inside of the air conditioner into an electric component room, in which the compressor 40 may be disposed and a heat-exchange room in which the axial fan 100 may be disposed.

An air suction inlet 15, into which external air may be suctioned, and an air discharge outlet 16, through which the air heat-exchanged in the heat-exchanger 20 may be discharged, may be disposed in the case 11. For example, the air suction inlet 15 may be disposed in a rear surface portion or rear surface and a side surface portion or side surface of the case 11, and the air discharge outlet 16 may be disposed in a front surface portion or side surface of the case 11.

The heat-exchanger 20 may be disposed inside of the case 11 to allow external air to be heat-exchanged with a refrigerant. The heat-exchanger 20 may be bent from one side of the axial fan 100.

FIGS. 2 to 4 are views of an axial fan according to an embodiment. Referring to FIGS. 2 to 4, the axial fan 100 according to an embodiment may include a hub 110 disposed to be rotatable by a central shaft 110 a, and a plurality of blades 120 coupled to an outside of the hub 110. The central shaft 110 a may be rotatable coupled to the motor.

The hub 110 may have a cylindrical shape or a circular pillar shape. In detail, the hub 110 may include a front surface portion 112 that defines a front surface of the hub 110, a rear surface portion 114 that defines a rear surface of the hub 110, and an outer circumferential surface portion 113 that defines an outer circumferential surface of the cylinder.

The front surface or a front side of the hub 110 may represent a direction in which air is blown, that is, a direction in which air is suctioned in, and the rear surface or a rear side of the hub 110 may represent a direction in which air is discharged. Hereinafter, description regarding these directions of the axial fan will be applied.

The blade 120 may include a first wing part or first wing 130 that extends with a first preset or predetermined curvature (gradient) from a tip 123 toward the hub 110, and a second wing part or second wing 140 that extends with a second preset or predetermined curvature (gradient) from the first wing part 130 toward the hub 110. The first and second preset curvatures may be different from each other. In detail, an angle defined by the first wing part 130 and a central axis of the hub 110 may be greater than an angle defined by the second wing part 140 and the central axis of the hub 110.

A boundary portion or boundary 135 may be defined between the first wing part 130 and the second wing part 140. That is, the boundary portion 135 may be a line that distinguishes the first wing part 130 from the second wing part 140. The second wing part 140 may have a shape which is rather sharply bent from the boundary portion 135 towards the hub 110, that is, towards the front surface portion 112 of the hub 110. Thus, the boundary portion 135 may be called a “bent portion”.

The first wing part 130 may be called an “outer wing part” or “outer wing”, and the second wing part 140 may be called an “inner wing part” or “inner wing”. For example, the first and second wing parts 130 and 140 may be integrated with each other.

The blade 120 may include a hub connection part or portion 121 coupled to the outer circumferential surface portion 113 of the hub 110, and tip 123 that defines an end of the blade 120. The hub connection part 121 may define an inner end of the blade 120, and the tip 123 may define an outer end of the blade 120. The tip 123 may be disposed on an outer end of the first wing part 130, and the hub connection part 121 may be disposed on an inner end of the second wing part 140.

The blade 120 may include a leading edge 125 that defines a front end in a rotational direction thereof, and a trailing edge 126 that defines a rear end in the rotational direction. In FIG. 3, the axial fan 100 may rotate in a counterclockwise direction.

The blade 120 may include a positive pressure surface 127 that faces an air blowing direction, and a negative pressure surface 128 that faces an air discharge direction. The pressure surface 127 may be understood as a surface that faces a front side to receive a pressure of air, and the negative pressure surface 128 may be understood as a surface that faces a rear side, that is, a surface opposite to the pressure surface 127.

When the tip 123 of each of the plurality of blades 120 extends in a clockwise or counterclockwise direction, a virtual circle C may be defined. A distance from a center of the hub 110 or the central shaft 110 a to an outer circumference of the virtual circle C, that is, a radius of the axial fan 100 may be referred to as R1. A distance from the center of the hub 110 or the central shaft 110 a to the outer circumference of the hub 110, that is, a radius of the hub 110 may be referred to as R2.

The hub 110 may have a relatively small size in comparison to a total size of the axial fan 100. In detail, the outer circumferential surface portion 113 of the hub 110 defines one sidewall of a passage through which air may pass when the axial fan 100 rotates. The outer circumferential surface portion 113 of the hub 110 may be parallel to an air flow direction to cause friction with air. Thus, a flow separation phenomenon may occur due to the friction, deteriorating fan efficiency. Thus, when the hub 110 has a relatively large size in comparison to the total size of the axial fan 100, a friction area may increase. As a result, the air passage may have a narrow width deteriorating performance of the axial fan 100.

Therefore, in this embodiment, a relative size of the hub 110 may be determined so that a ratio of R2 to R1 is in a range of about 10% to about 25%. That is, in comparison to axial fans according to the related art, the hub may have a relatively small size.

As described above, as the hub 110 has the relatively small size, the friction force occurring between the air flow and the hub 110 may be reduced. Thus, generation of a vortex may be prevented improving the fan efficiency.

FIG. 5 is a cross-sectional view taken along line V-V of FIG. 2. FIG. 6 is a view of a hub connection part of a blade according to an embodiment.

Referring to FIGS. 5 to 6, the outer circumferential surface portion 113 of the hub 110, to which the central shaft 110 a may be coupled, and the plurality of blades 120 coupled to the outer circumferential surface portion 113 may form the axial fan 100 according to an embodiment. Each of the blades 120 may include hub connection part 121 coupled to the outer circumferential surface portion 113 of the hub 110. The hub connection part 121 may define the inner end of the blade 120.

A portion at which the hub connection part 121 and the outer circumferential surface portion 113 of the hub 110 are coupled may have an area that is variable along the outer circumferential surface portion 113. That is, as shown in FIG. 6, a portion at which the hub connection part 121 and the outer circumferential surface portion 113 of the hub 110 are coupled has an area that gradually increases in a counterclockwise direction and gradually decreases in a clockwise direction.

In detail, the hub connection part 121 may include a front end 121 a disposed on or at a side of the front surface portion 112 of the hub 110, and a rear end 121 b disposed on or at a side of the rear surface portion 114 of the hub 110. In detail, the front end 121 a may extend adjacent to the front surface portion 112 of the hub 110, and a rear end 121 b may extend adjacent to the rear surface portion 114 of the hub 110. The front end 121 a may be understood as a portion that faces a front side of the hub connection part 121, and the rear end 121 b may be understood as a portion that faces a rear side of the hub connection part 121.

The front end 121 a may extend approximately parallel along the outer circumferential surface of the front surface portion 112, and the rear end 121 b may extend at an incline with respect to the rear surface portion 114. Thus, a distance between the front and rear ends 121 a and 121 b may gradually increase in a counterclockwise direction and gradually decrease in a clockwise direction on the outer circumferential surface portion 113 of the hub 110.

As described above, the hub connection part 121 may have a variable coupling area where it is coupled to the outer circumferential surface portion 113 of the hub 110 in a clockwise or counterclockwise direction. Thus, the blade 120 may be stably coupled to the outer circumferential surface portion 113 of the hub 110.

FIG. 7 is a view of the first wing part and the second wing part of a blade according to an embodiment. Referring to FIG. 7, the second wing part 140 according to an embodiment may extend from the first wing part 130 towards the outer circumferential surface portion 113 of the hub 110. The second wing part 140 may be bent in one direction with respect to a center at the boundary portion 135. Thus, with respect to a direction perpendicular to the central shaft 110 a of the hub 110, an extending direction of the first wing part 130, that is, a curvature or gradient of the first wing part 130 may be formed different from a curvature or gradient of the second wing part 140.

In detail, the blade 120 may include leading edge 125 that defines the front end in the rotational direction, and trailing edge 126 that defines the rear end in the rotational direction. The leading edge 125 may include a first leading edge 125 a disposed on the first wing part 130 and a second leading edge 125 b disposed on the second wing part 140. The trailing edge 126 may include a first trailing edge 126 a disposed on the first wing part 130, and a second trailing edge 126 b indisposed on the second wing part 140. The first and second leading edges 125 a and 125 b and the first and second trailing edges 126 a and 126 b may be distinguished from each other with respect to the boundary portion 135.

The second trailing edge 126 b may extend in a direction corresponding to an extension direction of the first trailing edge 126 a. That is, the second trailing edge 126 b may extend from the first trailing edge 126 a to the hub 110 in a state in which the second trailing edge 126 b is not bent.

In summary, an angle at which the second wing part 140 is bent from the first wing part 130, that is, a bent angle at a position at which the boundary portion 135 contacts the rear trailing edge 126 may be about 0°. The position at which the boundary portion 135 contacts the rear trailing edge 126 may be defined as a first end 135 a. On the other hand, the second leading edge 125 b is bent in a predetermined direction with respect to the extension device of the first leading edge 125 a to extend to the hub 110. In FIG. 7, the extension direction of the first leading edge 125 a is denoted by a virtual line la, and the extension direction of the second leading edge 125 b has a set angle θ1 with respect to the line la.

That is, an angle at which the first wing part 130 is bent from the second wing part 140, that is, a bent angle at a position at which the boundary portion 135 contacts the leading edge 125 may be about 61. For example, the bent angle θ1 may range from about 50° to about 70°. The position at which the boundary portion 135 contacts the front leading edge 125 may be defined as a second end 135 b.

In summary, although the blade 120 is not bent at the first end 135 a of the boundary portion 135, the blade 120 may be bent somewhat at the second end 135 b of the boundary portion 135. In other words, an angle at which the second wing part 140 is bent from the second end 135 b may be greater than an angle at which the second wing part 140 is bent from the first end 135 a. As a result, the second wing part 140 may extend in a direction corresponding to an extension direction of the first wing part 130 from the trailing edge 126. On the other hand, the bent angle in the extension direction of the first wing part 130 may gradually increase towards the leading edge 125.

According to the above-described components, the blade 120 according to this embodiment may have a large pitch angle. Thus, an amount of air achieved by the rotation of the wings may be sufficiently secured. This will be described hereinafter with reference to the accompanying drawings.

FIGS. 8A to 8C are views illustrating a shape of a pitch angle of a blade according to embodiments, when the second wing part is not adopted in the blade. FIGS. 9A to 9C are views illustrating a shape of the pitch angle of a blade according to embodiments, when the second wing part is adopted in the blade.

FIGS. 8A to 8C illustrate a state in which a pitch angle gradually decreases toward an inside of the blade, that is, the hub when a blade shape according to the related art is adopted (α1>α2>α3). Here, the pitch angle may be understood as an angle of a part of the blade with respect to a horizontal surface or horizontal line I1.

Also, the horizontal surface or horizontal line may be understood as a surface or line that is perpendicular to the central axis of the hub.

In detail, FIG. 8A illustrates a state in which the pitch angle of a tip of the blade is α1, and FIG. 8B illustrates a state in which the pitch angle defined at a radius position that corresponds to about 70% of the blade from the center of the hub is α2. Here, the radius position of about 70% may be understood as a position corresponding to about 70% of a distance from the hub to the tip of the blade.

FIG. 8C illustrates a state in which the pitch angle defined at a radius position that corresponds to about 40% of the blade 120 from the center of the hub is α2. The pitch angles α1, α2, and α3 may be expressed by the following relational equation.

α1<α2<α3

That is, in the case of the blade shape according to the related art, the pitch angle gradually decreases toward an inside of the blade. In this case, as the rotational force of the blade acting on air is less, fan performance may be deteriorated, and noise may increase.

FIGS. 9A to 9C illustrate a state in which the pitch angle gradually increases toward an inside of the blade 120, that is, the hub 110 when the blade shape according to embodiments disclosed herein is adopted. FIG. 9A illustrates a state in which a pitch angle of the tip 123 of the blade 120 is β1, and FIG. 9B illustrates a state in which the pitch angle defined at a radius position that corresponds to about 70% of the blade 120 from the center of the hub 110 is β2. FIG. 9C illustrates a state in which the pitch angle defined at a radius position that corresponds to about 40% of the blade 120 from the center of the hub 110 is β3.

The pitch angles β1, β2, and β3 may be expressed by the following relational equation.

β1>β2>β3

That is, in the case of the blade shape according to embodiments disclosed herein, the pitch angle gradually increases toward the inside of the blade. In this case, as the rotational force of the blade acting on the air is great, the fan performance may be improved, and noise may be reduced.

FIG. 10 is a graph of results obtained by comparing changes in power consumption of the axial fan according to the related art and the axial fan according to an embodiment. FIG. 11 is a graph of results obtained by comparing changes in noise of the axial fan according to the related art and the axial fan according to an embodiment.

Referring to FIG. 10, an amount of air is defined as an X-axis, and power consumption due to an operation of the axial fan is defined as a Y-axis. As the air amount increases, the power consumption tends to increase. Also, it is seen that an increasing degree in the power consumption is smaller in the case of adopting the axial fan according to an embodiment disclosed herein when compared to the case of adopting the axial fan according to the related art. Therefore, when the axial fan according to an embodiment disclosed herein operates, the power consumption may be reduced in comparison to the axial fan according to the related art.

Referring to FIG. 11, an amount of air is defined as an X-axis, and noise values caused by operation of the axial fan are defined as a Y-axis. As the air amount increases, the noise values tend to increase. Also, it is seen that an increasing degree in noise is smaller in the case of adopting the axial fan according to an embodiment disclosed herein when compared to the case of adopting the axial fan according to the related art. Therefore, when the axial fan according to an embodiment disclosed herein operates, noise may be reduced in comparison to the axial fan according to the related art.

FIG. 12 is a graphic view illustrating vorticity occurring around an axial fan when the axial fan according to the related art operates. FIG. 13 is a graphic view illustrating vorticity occurring around an axial fan when the axial fan according to an embodiment disclosed herein operates.

Referring to FIG. 12, when the axial fan according to the related art operates, an unsteady flow as shown by reference symbol S1, that is, a strong vortex is generated by a flow separation phenomenon due to air friction around the hub 110. In addition, it is seen that unsteady flow is generated at a side of the tip of the blade due to the influence of the strong vortex as shown by reference symbol S1.

On the other hand, referring to FIG. 13, when the axial fan according to an embodiment disclosed herein operates, it is seen that the vorticity generated around the axial fan, that is, the hub 110 and the tip 123 of the blade 120 is smaller in comparison to the case of FIG. 12.

As described above, the axial fan according to embodiments may have a relatively small hub height or diameter and include blades having first and second wing parts curvatures or gradients which may be different from each other. Thus, the vortex that may occur around the fan may be prevented.

According to embodiments disclosed herein, as the hub has a relatively small height and diameter, and the first and second wing parts of the blade are improved in structure, operation efficiency of the axial fan may be improved, and flow noise may be reduced. More particularly, the second wing part having the curvature different from that of the first wing part including the tip of the blade may be disposed inside the first wing part with respect to the boundary portion as a center, and the second wing part may be coupled to the hub. Therefore, the axial fan may be compact to increase the flow area of the air passing through the outside of the hub.

Also, the front end of the hub connection part disposed on the second wing part may be disposed adjacent to the front surface portion of the hub, and the rear end of the hub connection part may be inclinedly disposed so that the rear end is closer to the rear surface portion of the hub. Therefore, even though the hub decreases in height, a large pitch angle of the blade may be maintained. Also, as the hub has a small size, costs required to manufacture the hub may be reduced.

Embodiments disclosed herein provide an axial fan that has improved fan efficiency and reduced flow noise.

Embodiments disclosed herein provide an axial fan that may include a hub, to which a central shaft may be coupled, and a plurality of blades coupled to an outside of the hub. Each blade may include a hub connection part or portion that defines an end or a first end of the blade, the hub connection part being coupled to an outer circumferential surface portion or outer circumferential surface of the hub; a tip that defines the other or a second end of the blade; a first wing part that extends at a first preset or predetermined gradient from the tip; and a second wing part or second wing that extends from the first wing part towards the hub, the second wing part having a second preset or predetermined gradient.

The hub may have a cylindrical shape, and the hub may include a front surface portion or front surface that faces an air blow direction; a rear surface portion or rear surface that faces an air discharge direction; and an outer circumferential surface portion or outer circumferential surface that defines an outer circumference of the cylindrical shape. The blade may include a boundary portion or boundary that divides the first wing part from the second wing part, and the second wing part may be bent from the boundary portion towards the front surface portion of the hub.

The blade may include a leading edge that defines an front end in a rotational direction, and a trailing edge that defines a rear end in the rotational direction. The boundary portion may include a first end that contacts the trailing edge, and a second end that contacts the leading edge.

An angle at which the second wing part is bent from the second end portion may be greater than an angle at which the second wing part is bent from the first end. Further, the second wing part may extend from the first end to the hub in a direction corresponding to an extension direction of the first wing part and be bent at a preset or predetermined angle to extend from the second end in the extension direction of the first wing part. The angle bent from the first wing part toward the second wing part may be about 0° at the first end and may range from about 50° to about 70° at the second end.

An area of a portion at which the hub connection part and the outer circumferential surface portion of the hub are coupled may be variable in a clockwise or counterclockwise direction. The hub connection part may include a front end that extends along the front surface portion of the hub, and a rear end that extends inclined or at an incline with respect to the rear surface portion of the hub.

A distance between the front end and the rear end may gradually increase in the counterclockwise direction of the outer circumferential surface portion of the hug and gradually decrease in the clockwise direction of the outer circumferential surface portion of the hub. A virtual circle (C) that connects tips of the plurality of blades to each other may be defined, and a ratio of a radius (R2) of the virtual circle to a radius (R2) of the outer circumferential surface portion from a center of the hub may range from about 10% to about 25%.

The first and second wing parts may be integrated with each other.

Embodiments disclosed herein further provide an axial fan that may include a hub having a front surface portion or front surface, a rear surface portion or outer circumferential surface, and an outer circumferential surface portion; and a plurality of blades coupled to the outer circumferential surface portion of the hub. Each blade may include a tip that defines an outer end of the blade; an outer wing part or outer wing that extends at a first preset or predetermined gradient from the tip; an inner wing part or inner wing that extends from the outer wing part towards the hub, the inner wing part having a second preset or predetermined gradient; and a boundary portion or boundary defined between the outer wing part and the inner wing part. The boundary portion may be bent from the outer wing part toward the inner wing part. The first preset gradient and the second preset gradient may be different from each other.

The axial fan may further include a central shaft. An angle between the outer wing part and the central shaft may be greater than an angle between the inner wing part and the central shaft.

The blade may include a leading edge that defines a front end in a rotational direction, and a trailing edge that defines a rear end in the rotational direction. The boundary portion may include a first end that contacts the trailing edge, and a second end that contacts the leading edge. An angle at which the inner wing part is bent from the second end may be greater than an angle at which the inner wing part is bent from the first end. A pitch angle of the blade may gradually increase toward the hub.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.

Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art. 

What is claimed is:
 1. An axial fan, comprising: a hub to which a central shaft is coupled; and a plurality of blades coupled to the hub to rotate therewith, wherein each blade of the plurality of blades comprises: a hub connection portion that defines a first end of the respective blade, the hub connection portion being coupled to an outer circumferential surface of the hub; a tip that defines a second end of the blade; a first wing that extends at a first predetermined gradient from the tip; and a second wing that extends from the first wing towards the hub, the second wing having a second predetermined gradient.
 2. The axial fan according to claim 1, wherein the hub has a cylindrical shape, and wherein the hub comprises: a front surface that faces an air blow direction; a rear surface that faces an air discharge direction; and an outer circumferential surface that defines an outer circumference of the cylindrical shape.
 3. The axial fan according to claim 2, wherein each blade of the plurality of blades further comprises a boundary that divides the first wing from the second wing, and wherein the second wing is bent from the boundary towards the front surface of the hub.
 4. The axial fan according to claim 3, wherein each blade of the plurality of blades further comprises: a leading edge that defines a front end of the respective blade in a rotational direction; and a trailing edge that defines a rear end of the respective blade in the rotational direction, and wherein the boundary comprises: a first end formed at the trailing edge; and a second end formed at the leading edge.
 5. The axial fan according to claim 4, wherein an angle at which the second wing is bent from the second end is greater than an angle at which the second wing is bent from the first end.
 6. The axial fan according to claim 5, wherein the second wing extends from the first end to the hub in a direction corresponding to an extension direction of the first wing and is bent at a predetermined angle to extend from a second end in the extension direction of the first wing.
 7. The axial fan according to claim 6, wherein the angle between the first wing and the second wing is about 0° at the first end and substantially ranges from about 50° to about 70° at the second end.
 8. The axial fan according to claim 2, wherein an area of a portion at which the hub connection portion and the outer circumferential surface of the hub are coupled is variable in a clockwise or counterclockwise direction.
 9. The axial fan according to claim 8, wherein the hub connection portion comprises: a front end that extends along the front surface of the hub; and a rear end that extends at an incline with respect to the rear surface of the hub.
 10. The axial fan according to claim 9, wherein a distance between the front end and the rear end gradually increases in the counterclockwise direction of the outer circumferential surface of the hub and gradually decreases in the clockwise direction of the outer circumferential surface of the hub.
 11. The axial fan according to claim 2, wherein a virtual circle (C) that connects tips of the plurality of blades to each other is defined, and wherein a ratio of a radius (R1) of the virtual circle to a radius (R2) of the outer circumferential surface from a center of the hub ranges from about 10% to about 25%.
 12. The axial fan according to claim 1, wherein the first and second wings are integrated with each other.
 13. An outdoor device of an air conditioner comprising the axial fan of claim
 1. 14. An axial fan, comprising: a hub having a front surface, a rear surface, and an outer circumferential surface; and a plurality of blades coupled to the outer circumferential surface of the hub to rotate therewith, wherein each blade of the plurality of blades comprises: a tip that defines an outer end of the blade; an outer wing that extends at a first predetermined gradient from the tip; an inner wing that extends from the outer wing towards the hub, the inner wing having a second predetermined gradient; and a boundary defined between the outer wing and the inner wing, wherein the boundary is bent from the outer wing toward the inner wing.
 15. The axial fan according to claim 14, wherein the first predetermined gradient and the second predetermined gradient are different from each other.
 16. The axial fan according to claim 14, further comprising a central shaft to which the hub is coupled, wherein an angle between the outer wing and the central shaft is greater than an angle between the inner wing and the central shaft.
 17. The axial fan according to claim 14, wherein each blade of the plurality of blades further comprises a leading edge that defines a front end in a rotational direction and a trailing edge that defines a rear end in the rotational direction, wherein the boundary comprises a first end that contacts the trailing edge and a second end that contacts the leading edge, and wherein an angle at which the inner wing is bent from the second end is greater than an angle at which the inner wing is bent from the first end.
 18. The axial fan according to claim 14, wherein a pitch angle of the respective blade gradually increases toward the hub.
 19. An outdoor device of an air conditioner comprising the axial fan of claim
 14. 20. An axial fan, comprising: a hub to which a central shaft is coupled; and a plurality of blades coupled to the hub to rotate therewith, wherein each blade of the plurality of blades comprises: a first wing that extends at a first predetermined gradient from a tip; thereof; a second wing that extends from the first wing towards the hub, the second wing having a second predetermined gradient; and a boundary that divides the first wing from the second wing, and wherein the second wing is bent from the boundary towards a front surface of the hub.
 21. The axial fan according to claim 20, wherein each blade of the plurality of blades further comprises: a leading edge that defines a front end of the respective blade in a rotational direction; and a trailing edge that defines a rear end of the respective blade in the rotational direction, and wherein the boundary comprises: a first end formed at the trailing edge; and a second end formed at the leading edge, wherein an angle at which the second wing is bent from the second end is greater than an angle at which the second wing is bent from the first end.
 22. The axial fan according to claim 21, wherein the second wing extends from the first end to the hub in a direction corresponding to an extension direction of the first wing and is bent at a predetermined angle to extend from the second end in the extension direction of the first wing.
 23. The axial fan according to claim 22, wherein the angle between the first wing and the second wing is about 0° at the first end and substantially ranges from about 50° to about 70° at the second end.
 24. The axial fan according to claim 20, wherein a virtual circle (C) that connects tips of the plurality of blades to each other is defined, and wherein a ratio of a radius (R1) of the virtual circle to a radius (R2) of the outer circumferential surface from a center of the hub ranges from about 10% to about 25%.
 25. The axial fan according to claim 20, wherein the first and second wings are integrated with each other.
 26. An outdoor device of an air conditioner comprising the axial fan of claim
 20. 